1. Field of the Invention
This invention relates to a device for and a method of searching time code recorded on a disk-shaped recording medium on which discontinuous time codes are recorded.
2. Description of Prior Art
When picture information is recorded on a recording medium such as an optical disk or the like, it has been generally used a method in which time codes representing hour, minute, second and frame information are beforehand recorded on the recording medium together with the picture information, and an editing work of recorded information is carried out using these time codes to improve efficiency of the editing work. In the following description, a time code representing the time of 0 hour 0 minute 0 second 1 frame is expressed as "00:00:00:01".
The time codes can be freely set to any values, and thus it is frequent case that plural pieces of information are recorded on a recording medium with time codes having discontinuous values. For example, there is a case where a first information is recorded in a first recording area with time codes from "00:00:00:01" to "00:20:00:00" while a second information is recorded on a second recording area, adjacent to the first recording area, with time codes from "10:00:00:00" to "10:15:00:00". In this case, the time code "10:00:00:00" is recorded subsequently to the time code "00:20:00:00" at the boundary of the first and second recording areas, and thus the time code sequence becomes discontinuous at the boundary. Further, since the time code can be arbitrarily set, the each time codes set for the recorded information are not necessarily aligned on the recording medium in such a manner that the values thereof are gradually increased in a recording direction of the recording medium (for example, in a direction from the innermost peripheral side of an optical disk to the outermost peripheral side thereof). In addition, even when continuous time codes are recorded over the whole recording area of a recording medium, if the recorded information is edited and recorded on a new recording medium, the time codes recorded on the new recording medium become discontinuous.
In searching for a recording position of a desired time code in a conventional disk-type recording medium reproducing device such as a video disk player or the like, the time code search is carried out using frame addresses which are beforehand recorded on a disk-shaped recording medium (hereinafter referred to as "disk") used exclusively for reproduction (hereinafter referred to as "reproduction-only disk"). Here, "frame address" indicates an absolute address which is assigned to each frame or each track. For example, for a constant angular velocity (CAV) having a diameter of 30 cm, continuous frame addresses of "1" to "54000" are assigned in correspondence to first to 54000th tracks. The time codes are determined in accordance with the frame addresses in one-to-one correspondence. For example, for the above CAV disk, frame addresses "1" to "54000" correspond to the time codes "00:00:00:01" to "00:30:00:00" Therefore, as shown in FIG. 1, in a reproduction-only disk, the time codes can be easily converted to corresponding frame addresses.
An operation of the time code search will be described hereunder with reference to FIG. 2.
The disk-shaped recording medium reproducing device includes a pickup 1. The pickup 1 reads out an RF signal including a recorded picture information from a recording disk, and the read-out RF signal is supplied to a demodulator 2. The demodulator 2 demodulates the RF signal read out by the pickup 1 into a picture signal which includes information such as a frame address, a time code, on a vertical blanking period and supplies the demodulated signal to a frame address detection device (referred to as "FA detection device 3").
The frame address detection device 3 detects a frame address on the basis of the demodulated signal and supplies the frame address to a latch 7. For example, the frame address detection circuit 3 detects the frame address "10000" and supplies it to the latch 7. A key input device 5 is provided with, for example, a push button on a front panel (not shown). The key input device receives a user's input of time code to be searched and outputs the inputted time code to a conversion device 6. For example, the key input device 5 supplies a time code="00:10:00:00" to the conversion device 6.
The conversion device 6 converts the time code supplied from the key input device 5 into a frame address. For example, a time code="00:10:00:00" is converted to the corresponding frame address="18000". This frame address="18000" becomes a target frame address for search, and is supplied to a comparator 8.
When a switch SW1 on a front panel (not shown) is set to a closed state, a time code search start signal which is usually in a "H"-level is set to a "L"-level during the closed state of the switch SW1. A search start signal generator (MMV: Mono-Multi Vibrator) 4 detects the trailing edge of the time code search start signal and supplies a search start signal having a predetermined pulse width to the latch 7 and a search control device 9.
Upon receipt of the search start signal, the latch 7 detects the rising edge of the search start signal to latch a frame address corresponding to a current reproducing position of the pickup 1 (hereinafter referred to as "current frame address") at the timing of the rising edge. For example, a frame address="10000" is latched as a current frame address. The latched current frame address is supplied to the comparator 8 to compare the inputted current frame address with the target frame address which has been previously fed to the comparator 8, and a difference between the current frame address and the target frame address (="+8000") is supplied to the search control device 9. The absolute value of the difference (="8000") represents a distance at which the reproducing position of the pickup 1 should be shifted (hereinafter referred to as "shift distance"), and a sign (polarity)="+"located before the numeral represents a direction to be shifted (hereinafter referred to as "shift direction"). In the following description, the polarity "+"represents the shift of the reproducing position of the pickup 1 in an outer peripheral direction of the disk (i.e., toward the outermost peripheral side of the disk), and the polarity "-" represents the shift of the reproducing position of the pickup 1 in an inner peripheral direction of the disk (i.e., toward the innermost peripheral side of the disk).
The search control device 9 includes a direction setting device 9a, a comparator 9b, a shift amount detection device 9c, a speed setting device 9d and a search termination signal generator 9e. The direction setting device 9a sets a shift direction of the pickup 1 in a radial direction of the disk on the basis of the polarity of the difference supplied from the comparator 8, and the output thereof is transmitted to a driver circuit 10 for controlling a slider motor. The comparator 9b outputs a shift distance supplied from the comparator 8. The shift amount detection device 9c includes a position detector, a counter for counting a detection pulse of the position detector, etc., and detects and outputs a shift amount. The speed setting device 9d sets a proper shift speed for the difference signal (residual or remaining shift distance) between the output of the comparator 9b and the output of the shift amount detection device 9c, and an output signal thereof is supplied to the drive circuit 10 to drive the slider motor 11 on the basis of this signal.
Upon receipt of the search start signal, the output of the search termination signal generator 9e is set to "H"-level. In response to this signal, the drive circuit 10 outputs the control signal to the slider motor 11, and the pickup 1 starts moving in the radial direction of the disk in accordance with the output signal of the drive circuit 10. According to the shift of the pickup 1, the output of the shift amount detection device 9c is varied, and remaining shift distance obtained from the comparator 9b is decreased. The shift speed corresponding to the remaining shift distance is set in the speed setting device 9d, and the slider motor 11 is controlled in accordance with the set shift speed. Upon detection of the state that the remaining shift distance becomes equal to "0" on the basis of the signal from the comparator 9b, the search termination signal generator 9e outputs a "L"-level search termination signal. The search termination signal is supplied to the drive circuit 10 and a tracking control device (not shown). As a result, the output of the control signal from the drive circuit 10 is inhibited or fixed to a predetermined constant level. Upon receipt of the search termination signal, the tracking control device (not shown) carries out a tracking control and the search operation is terminated.
In the searching method as described above, it is necessary that the time codes are continuously recorded proportional to the frame addresses so as to be easily converted to the frame addresses. As a result, this method is not applicable to a recording medium such as an edited medium after edition in which the time codes are not recorded proportionally or in one-to-one correspondence to the frame addresses.